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ADDRESSES DELIVERED AT THE CONVENTION OF THE NATIONAL SHELLFISHERIES ASSOCIATION

Washington, D. C. August 1) = 16, 1951

James Nelson Gowanloch James B. Engle President Vice-President

A. F. Chestnut Secretary

Published for the National Shellfisheries Association by the Fish and Wildlife Service, U. S. Department of the Interior

Washington July 1953

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TABLE OF CONTENTS

1951 ADDRESSES

Title Page

Seasonal Variations of Coliforms and Enterococci in a Closed Shellfish Area William Arcisz, Elsie Wattie, James L. Dallas it

Notes on Growth of Thais haemastoma floridana and Thais (Stramonita) rustica Robert M. Ingle 12

A Method of Reducing Winter Mortalities of Venus Mercenaria in Maine Waters Robert L. Dow and Dana E. Wallace 15

Incidence of Infection of Oysters by Dermocystidium in the Barataria Bay Area of Louisiana J. G. Mackin 22

A Report on the Interrelationship Between the Growth and Mortality of Oysters H. Malcolm Owen and Lester L. Walters 36

The Effects of Predation on Soft Clams, Mya Arenaria Osgood R. Smith and Edward Chin 37

Variations in Sizes and Rate of Growth of Lamellibranch Larvae of the Same Parents Robert R. Marak Ty)

The Bonnet Carré Spillway and the Oyster Beds of Mississippi Sound Gordon Gunter 6

Biological Effects of Bullraking vs. Power Dredging on a Population of Hard Shell Clams, Venus Mercenaria John B. Glude and Warren S. Landers 7

Oyster Condition Affected by Attached Mussels James B, Engle and Charles R. Chapman 70

Some Factors Influencing Steam Yields in Oysters Francis X. Lueth 79

TABLE OF OONTENTS

1951 ADDRESSES

Title Page

Studies of the North Carolina Clam Industry A. F. Chestnut 85

A Soft Clam Population Census in Sagadahoc Bay, Maine 1949=?50='51 Harlan S. Spear 89

SEASONAL VARIATIONS OF COLIFORMS AND ENTEROCOCCI IN A CLOSED SHELLFISH AREA

William Arcisz, Elsie Wattie, James L. Dallas U. S. Public Health Service, Shellfish Sanitation Laboratory, Woods Hole, Massachusetts

Many valuable shellfish resources cannot be utilized because they exist in polluted waters near seashore communities. Some of these communities have a stable population contributing a uniform yearly pollution. Others, such as summer resorts, have widely fluctuating populations, and contribute varying amounts of pollution to the receiv- ing waters. A vital question is raised concerning restriction of shell- fish gathering after the summer population has gone and the pollution is materially reduced.

The purpose of this study was to determine, (1) the year-round variability of the quality of both water and shellfish from an area with such a seasonal fluctuation in population, and (2) the ratio of pollu- tional organisms present in the overlying water and in the shellfish. The study consisted of a sanitary and bacteriological survey.

Sanitary Survey of Eel Pond

Description

Eel Pond (see Figure 1), situated in the center of Woods Hole, Massachusetts, has an area of approximately 0.025 sq. mi., and a water- shed area of approximately 0.28 sq. mi. The pond, varying in depth from about two feet at the shore to 20 feet in the center, has about 80 per- cent of the shore line well defined.by vertical stone walls. Three fresh water inlets, one on the east side, two on the north side, numerous sur- face drains, and some private sewers, discharge into the pond.

The land immediately surrounding Eel Pond is fully developed. On the immediate shores are located domestic dwellings, stores, bakeries, restaurants and biological laboratories. The pond provides an excellent harborage for large and small pleasure carft, and is used as such all year round; naturally, the numbers of such craft increase greatly during the summer,

Eel pond is directly connected to Great Harbor by a boat channel about 500 feet long and 75 feet wide. Current observations made at the Eel Pond outlet to this channel during a 6-hour period revealed 18 cyclic changes of current flow with a maximum velocity of about one foot per second. This fluctuation of current, coupled with the mean range of tide which is 1.8 feet, indicates that the pond seldom gets a thorough flushing. Thus, it appears that the pollution in the pond has a tendency to be maintained at a high level.

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Sanitary Survey

A sanitary survey of the immediate vicinity of Eel Pond shows that there are 90 homes and establishments which contribute pollution either directly or indirectly into the pond. There is an increase in the pollution load inthe sunmer due to summer residents. It is estimated that the population in the immediate vicinity of Eel Pond increases to 2,200 during the months of June, July and August, as compared to 00 year-round residents. Although most of the homes bordering on the pond have cesspools, there are a few which discharge their sewage directly into the pond. Seepage and overflow from a number of the cesspools cause some pollution of the pond. The waters of Great Harbor near the Eel Pond boat channel receive considerable pollution from commercial establishments and dwellings along the channel. Some of this pollution probably enters Eel Pond during the flood tide.

On the basis of the sanitary survey, it would appear that Eel Pond is subject to moderate pollution throughout the year with a marked increase during the months of June, July and August.

Bacteriological Survey

A series of six stations (Figure 1) was established in Eel Pond; one in the approximate center, one at the entrance of the boat channel, and four at approximately equidistant points along the periphery of the pond. Surface water samples were collected at these stations at least once a month from August 198 through July 1950. Additional samples were collected for salinity determinations. At one station (Captain Kidd's), in addition to the water samples, a shellfish sample consisting of six or more quahogs (Venus mercenaria) was collected for bacteriological examination. The temperature of the water was determined at each col- lection.

Laboratory Methods

Samples of shellfish and water were collected and prepared for analysis, except for a few minor deviations, in accordance with the methods described in "Recommended Procedure for the Bacteriological Examination of Shellfish and Shellfish Waters".

Phosphate dilution water (2) was used instead of one percent salins. Shellfish were prepared for disintegration in a Waring Blendor by weigh- ing the contents of six shellfish and adding an equal amount by weight of sterile phosphate buffered diluent instead of the recommended 200 ml. of one percent saline to 200 ml. of meats and liquor.

Suitable aliquot portions of samples were planted in at least three decimal dilutions using five tubes per dilution. Parallel plantings ey° made into standard lactose broth and Winter and Sandholzer enterococcus presumptive broth. The presumptive lactose broth tubes were incubated at 37° C. (air incubator) and examined for the presence of gas at 2l and 48 hours. All lactose broth tubes showing gas were confirmed by transferring a 3 mm. loop= ful to brilliant green lactose bile broth 2% (B.G.B.). The presence of gas in any amount in B.G.B. after 2h or 48 hours of incubation at 37° C. was considered a positive test for the coliform group.

The enterococcus presumptive broth tubes were incubated for 2h hours in a 5* C. (water bath) and examined for turbidity and acid which indicate a positive presumptive test. Positive presumptive tubes were checked by transferring two loopfuls (3mm. loop) to con= firmatory agar-broth slants for incubation at 37° C.-for 18 to 2h hours. The confirmed test consisted of: (1) pin-point colonies on the agar slant, (2) sedimented growth in the broth portion, and (3) the demonstrations of gram positive streptococci. oe oo. were recorded in terms of the "Most Probable Number" (MPN) 3 per 100 ml. for members of the coliform and enterococcus groups.

Results

In Figure 2, the average MPN values for coliforms and enterococci and the average monthly temperatures for Stations 1 through 5 are presented.

In general, the coliform content of the waters follows the tempera- ture fluctuations, however, this condition is not constant. The sharp rise of coliforms and enterococci in April as compared to March and May might be due to a temporary increase in population. Summer residents often come to Woods Hole in April to inspect their homes and to make the necessary preparations for reopening themin June. During June, July and August, when the population of Woods Hole is at its peak, the coliform content of the water increases. Since the recovery of enterococci, with one exception, is low (not more than 10 organisms per 100 ml.), it seems that no conclusions regarding the effect of temperature on the numbers of organisms of this group of bacteria can be made.

Figure 3 shows the average coliform and enterococcus values of waters and quahogs from the Captain Kidd station.

In December, January, February, March and April the coliform content of quahogs was considerably below the 200 per 100 ml.5 Public Health Service's tentative coliform standard for shellfish other than oysters. For the most part, however, the overlying water during the period is in grossly polluted range, having a coliform content of 700 or more per 100 ml. Quahogs are inactive at temperatures of C. or

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lower and it is interesting to note that, during the cold months, the coliform content of these shellfish was significantly low.

With the advent of higher temperatures an increase in the coliform and enterococcus content of the quahog was observed. A simultaneous rise and fall of the coliform content and ube) (EAP esaEEre is noted. These data are in agreement with Loosanoff's observations. Using "shell openness" asa measure of activity he found that hibernation, for a majority of quahogs examined, began at 5.0° to 6.0° C. At tempera- tures of 3.9° to 10.0° C. he found there was a correlation with period of openness and the rise in mean temperature. He found no correlation when the temperature of the overlying water was in the range of 11° to 27.9*° C. However, he did find that the animals were open 69 to 90 percent of the times; the highest percentage of openness, 90%, occurred at tempera- tures between 21 and 22° C. These observations are borne out in Figure 3.

A rise in temperature and an increase in population is reflected in the coliform and enterococcus densities of water and quahog samples. The maximum numbers of these bacteria occur in June, July and August when Woods Hole has its maximum population. Although the coliform and entero- coccus groups of organisms follow a similar pattern, no constant ratio exists between them.

In Figure ), the mean monthly coliform and enterococcus content of waters from Stations 1 through 5 are compared with those from Captain Kidd's. The rise and fall of coliforms at both sampling areas show a Similar pattern. However, the above trend is not apparent in the enterococcus results.

The average salinities and coliform and enterococcus numbers from Stations 1 through 5 and Captain Kidd's are presented in Table I. There is no marked variation of salinity during the course of the year. The salinity of the pond is slightly less than that of Vineyard Sound, the outer boundary of Great Harbor. The salinity of Eel Pond has no apparent

effect on the bacteriological population.

In Figure 5, the effect of population on the coliform and entero- coccus densities in samples from the Captain Kidd station is shown. During the summer months of June, July and August the approximate popu- lation discharging wastes in the immediate area of this station is 1,000, as compared to 75 during the remainder of the year. The popula- tion density increases in an approximate ratio of 13 to 13; the coliform and enterococcus ratios increase only three to one.

Discussion and Conclusions

The data indicate that when the population contributing pollutions increases, the coliform and enterococcus organisms in quahogs also increase. Quahogs (Venus mercenaria) are quiescent at temperatures of 5°C. or less. The results show that the bacterial content of the

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FIGS

COLIFORM. ENTEROCOCCUS&.

POPULATION DENSITIES

CAPTAIN KIDD EEL POND 1948 - 1950

LEGEND

COLIFORM JUNE -AUGUST MPN/ IOOML SEPT - MAY

POPULATION

ENTEROCOCCUS MPN./100 ML

Average Salinities, Coliforms and Enterococci from Eel Pond

Salinity

Eiibchlie

30.867 29.972

28.251

Table I

Water Samples _

Coliforms Enterococci

MPN /100 ml MPN/100 ml

150 3-1 4gg 9-8 298 2.9 1,048 era 208 2.5 1,016 7.8 931 5-5 1,075 See 6ule 4.6 263 ye) 415 Lee 558 10.2

10

Salinity

Tele oils

31.333 30.840 27 -850 31.770 30.820 31.550 31.620 31.236 31.400 31.790 30.925 31.330

Coliforms

MPN/100 ml

965 2,940 1,730 4, 900

hoe 3,820 10,500 9,300 2,720 1,610 1,060

1/00

Enterococci

MPN/100 ml 13.1 36.6 20.6

9.3 19.0 29.7 51.0

119.0 21.6 14.0 14.0

31.0

shellfish is not affected under such conditions by the quality of the overlying waters. As soon as the temperature rises and the quahogs become active, their coliform and enterococcus contents are affected by the coliform and enterococcus density of the overlying water.

The salinity of the waters in Eel Pond, ranging from a low of 27 parts per thousand to a high of 32 parts per thousand, indicate that comparatively little fresh water enters Eel Pond.

From the available data there is an indication that no ratio exists between the coliform and enterococcus groups of organisms. The findings of the sanitary survey also indicate that Eel Pond is seldom flushed.

The results of the sanitary and the bacteriological survey show that although Eel Pond is polluted at all seasons of the year, the pollution is greatest during June, July and August when the population of the community increases. However, when the population decreases, the pollution does not decrease sufficiently to permit harvesting or marketing of shellfish.

REFERENCES

1. American Public Health Association Recommended Procedure for the Bacteriological Examination of Shellfish and Shellfish Waters. Amer. Jour. Pub. Health, Vol. 37, No. 9, 197.

2. Butterfield, Cc. T. Experimental Studies of Natural Purification in Polluted Waters. VII The Selection of a Dilution Water for Bacteriological Examination. Reprint No. 1580, P. H.R. Vol. 8, No. 24, June 16, 1933, 681-691.

3. Hoskins, J. K. The most probable number for the evaluation of Coli- aerogenes tests by fermentation tube method. Public Health Repts. 9, 393, 193). Reprint No. 1621.

4. lLoosanoff, Victor L. Effect of temperature upon shell movements of clams, Venus mercenaria (L), Biol. Bull. 76, 171-182, 1939

5. Winter, C. E., and Sandholzer, L. A.

Recommended Procedure for Detecting the Presence of Enterococci. Commercial Fisheries TL2, Nov. 196

11

NOTES ON GROWTH OF THAIS HAEMASTOMA FLORIDANA AND THAIS (STRAMONITA) RUSTICA

Robert M. Ingle Marine Laboratory, University of Miami and Florida Division of Oyster Cultivation

In order to wage successful campaigns against predators, it is usually advantageous to know as much as possible about the bio-eco- logical backgrounds of such pests. Many times, weaknesses in the survival fitness are found which, if properly exploited, result in diminished numbers of the harmful organism and a reduction in its activity. Such considerations provided the motivation for a study of the growth rates of two of Florida's most voracious gastropod predators.

The location for these studies was the area surrounding the mouth of the local waterway, Coral Gables, Florida.

From February 22 to February 26, 1950, 257 snails of the genus Thais were notched on the lip and released. Of these, 181 were Thais haemastoma floridana and 76 were Thais (Stramonita) rustica.

On May 15 and 16, 1950, all marked animals that could be found were brought to the laboratory for measurement. Ten of these were Thais rustica and fourteen were Thais floridana, making a total of twenty-four recovered. Lip increment was then determined. j

As shown by Moore (6-7), the relation between the amount of growth measured in a spiral direction on the lip of a shell and the correspond- ing increase in the height of the shell is dependent on two fundamental shell angles, theta, the half apical angle, and alpha, the spiral angle. Theta may be obtained by direct measurement, but alpha is usually obtained from the formula:

tan alpha 2 2./2 sin theta, where log R

Ris the ratio of the diameters of two successive whorls. The formula

for determining the length of a plain logarithmic spiral is 1 = sec alpha. ip

If this spiral is projected upon a cone (as it is in the case of the two

snails studied), the formula becomes:

1! * sec alpha. sec beta r

where 1' = the spirally measured length, and beta is an angle derived from alpha and theta, but more easily taken by direct measurement.

12

Table 1

Growth of Thais rustica (all figures given in mm)

Calculated final Original Whorl Height Weekly Height Inc, Measured Height Height 22 5250 mm 5-15-50 Ina, Inc. 2.00 16.0 Swe 9.4 8 33.6 10.5 38.7 pip 4 26.4 (fo 29).0 2.6 ee 28.2 Aig) BERS, (ee. 6 26.0 20.0 BIAS) 9.5 8 25.6 15.0 a7e5 11.9 1.0 2562 16.0 36.2 ESO 9 26.6 16.0 34.0 7.4 .6 29.1 8.0 IDet 46 4 26.5 iLibalo) Silas} Sed a4 2703 13.4 34.7 74 6 Growth of Thais floridansa Calculated Final Original Height Weekly Hei ght Whorl Measured Height Height 2-2 550 Inc, 5-16-50 Inc, Inc, 46,2 6.0 48,5 a | ae 42,0 16.5 50.0 9.0 .6 38.0 13.0 ML, 5 6.5 Bd 45,0 12.5 50.5 5E5 4 31.9 2540 43.0 11.1 ale) 34.3 15.0 4O.5 6.2 oa 35.8 et?) 41,0 SHE 4 3900 8,0 ime, Sy WHE 36.0 9,0 40.0 4,0 33 55, 8 9.5 40,0 4,2 “3 SUA) 20.0 40.0 9.9 7 27.8 35.0 40.0 12.2 1,0 33.2 11.0 39.0 5.8 55) Zoe 19,0 35.0 9.8 8 35.4 15.0 42.1 6.7 A

13

Frequently during the entire period of this study, females were noted laying eggs. It may be presumed that the growth recorded here takes place during the times of normal reproductive processes.

Results of growth rate sudies are given in Table 1. It will be seen that the average height increment for the ten Thais rustica was slightly greater (7. mm) than the average increase shown for Thais floridana (6.7 m). This slight difference is very likely the result of the smaller size of individuals making up the Thais rustica sample. More rapid lineal growth is a common feature of younger, smaller individuals.

In a period of 82 days maximum height increment for Thais floridana was 12.2 mm (approximately 1/2 inch). In the same length of time, the maximum recorded height growth for Thais rustica was 11.9 mn.

The faster rate of living, and growing, in warmer waters has been reported often by investigators of other poikilothermous animals. Oysters, in particular, have been shown by Ingle (3=)), Gunter (2), and Menzel (5) to have a very rapid growth in the Gulf of Mexico.

Experiments are being conducted at the present time to ascertain growth rate during the other seasons of the year.

REFERENCES

1. Clench, William J. 197. The Genera Purpura and Thais in the Western Atlantic. Johnsonia 2(23): 61-92.

2. Gunter, Gordon P. 1951. The West Indian Tree Oyster on the Louisiana Coast, and Notes on Growth of the Three Gulf Oysters. Science ALES} (29h) = 2516-517.

3. Ingle, Robert M. 1950. Growth of American Oyster in Florida Waters. Science 112 (2908) 2338-339.

he Ingle, Robert M. 1951. Winter growth of American Oyster in Florida Waters, In press.

5. Menzel, R. Winston, 1951. Early Sexual Development and Growth of the American Oyster in Louisiana Waters. Science 113(29h7): 119-720.

6. Moore, Hilary B. 1936. The Biology of Purpura lapillus I. Shell Variation in Relation to Environment. Journ. Mar. Biol. Assoc. of United Kingdom. 21261-89.

7. Moore, Hilary B. 1937. The Biology of Littorina littorea. Part I. Growth of the Shell and Tissues, Spawning, Length of Life and Mortality. Journ. Mar. Biol. Assoc. of United. Kingdom.

1,

A METHOD OF REDUCING WINTER MORTALITIES OF VENUS MERCENARTA IN MAINE WATERS

Robert L. Dow and Dana E. Wallace State of Maine Department of Sea and Shore Fisheries

This paper is primarily concerned with efforts to reduce winter mortalities of Venus mercenaria in Maine waters. During the last five years some work has been done on this problem, but the following discussion is of our more intensive efforts during the last year.

Maine does not have a very large hard-shell clam fishery in comparison with other Atlantic states; but, despite the annual take of only about half a million pounds of meats, or 50,000 bushels, at a value of approximately $100,000, it is an important part of the economy of towns that border on Casco Bay. It is primarily an intertidal fishery.

Our industry relies upon natural seed sets to support the fishery between periods of natural setting. From what information is available it appears that these intermittent sets have extended back into the 20's in this area, and how much longer we do not know. The last good set that we received in the upper portion of Casco Bay was in 197, and the bulk of this Venus population is just getting to littleneck size this summer. In some of the best growing sections, cherries of this same age class can be found.

Although the sets are infrequent, heavy concentrations of quahogs have, in the past, occurred in small areas. Under certain conditions these quahogs have grown relatively slow, and mortalities have been high. Transplanting of these quahogs has, for the most part, proved to be economically desirable because of high survivals and good growth of the relayed seed. Last summer we moved 3012 bushels from two areas of heavy concentration in Maquoit Bay.

Moving any numbers of quahogs of this size presented financial and other problems. Qur own Department did not have funds and could only supply personnel to aid in the organization and transplanting operations. Meetings were held with the diggers, town officials and dealers; and the diggers contributed their efforts for several tides. A special town meeting ear- marked town license money for some equipment used in moving the seed. Dealers in the area made $200 available; the Bount Seafood Corporation of Warren, Rhode Island contributed $500; and a $1000 contribution from the Campbell Soup people was added to pay for the transplanting of the seed. The operation extended from July 8 to December 6 and was terminated because of the cold weather. Quahogs were, for the most part, spread onto the flats near or below the mean low tideline.

15

Concentrations were found to run as high as 167 per square foot with Venus ranging from 27 - 59 mm. having a mean of 3 mm. Slide #1 illustrates the concentration of quahogs as does Slide #2 and Slide #3. In Slide #3 a pile has been made of quahogs from the area shown. Slide #l illustrates one of the methods of gathering. Quahogs were raked into windrows shoveled with the use of rock forks into wire baskets and then loaded into boats as shown in Slide #5 or bagged as shown in Slide #6. Quahogs were spread directly from the boats onto the flats or sifted out of bags from boats towed by put- board motors as shown in Slide #7. Slide #8 is a photograph of a chart showing the relative locations of the seed beds and the sections into which the quahogs were planted. Figures indicate the number of bushels relaid into the various areas. In order to record the population numbers and dis= tribution of the Venus in these concentrations a planimetric map was made of the two principal seed areas.

Slide #9 shows the telescopic alidade, plane table and surveyor's rod used in making the planimetric map. Slide #10 is a convenient rock inthe seed bed area that was used as a survey station. A map of the 1950 fall survey is shown in Slide #11. The dots on the map indicate where square- foot samples of Venus were taken, counted and measured. Boundaries of the area are shown.

Throughout the summer and at the time of the last transplanting on November 18 from Seed Bed #2, we observed that many quahogs were exposed, or partially so, because of excessive crowding and their inability to bur=- row to a normal depth in the flats. Slide #12 shows how sandy-clayey silt partially covered the quahogs in the depressions and how quahogs in the higher portions of the flats were completely covered by sediment. The edge of one of these higher portions of flats can be seen in the top left corner of the slide.

On November 25 and 26 of 1950, the Casco Bay area was lashed by a violent wind and rain storm with peak gusts of wind of 76 mp.h. occyrring near the time of low water on the twenty-sixth. Shortly after this storm we observed that most of the silt over and around the quahogs had been removed, and thousands of live quahogs were almost completely exposed to the elements. This was the condition when observed on December 2).

This area was again visited on February ). Excessive mortalities had occurred and a closeup of these empty valves is shown by Slide #13, with a view out across the flats show by slide #1.

We cannot be positive of the exact time and reason for the heavy mortalities of the sediment free, exposed quahogs in the seed beds found in the intertidal zone of Maquoit Bay, but we do feel that combinations of factors, including the water, tide and weather, as shown on Slide #15, have important bearing upon these mortalities, The amunt of ice over the beds, the rate of freezing and thawing, concerning which we have no information, may have had great significance.

16

At the bottom of the chart are the sea water temperatures in Fahrenheit degrees recorded by the Coast Guard Station at Portland Headlight in outer Casco Bay. They may be indicative of fluctuations in the temperature of. water that covered the quahog beds in the inner portion of the bay. All weather data shown were obtained from the U. S. Weather Bureau office eighteen miles southwest of Bunganuc Point in Portland. At the top of the graph are the dates, heights of the tides, the atmospheric pressures, and wind speeds and directions. On the left margin are shown the air tempera- tures in Fahrenheit degrees.

We considered that weather factors at the time of low water were most critical, so we selected the Weather Bureau's temperature, wind and atms-~ pheric pressure recordings that were made nearest to the time of each low water. Taking into consideration the observations of the local diggers as to the length of time that Seed Bed #2 is uncovered by the water on each low tide, it appeared that it would be best to compute all information on the basis of the Venus being exposed to the elements for an average time of four hours per low tide. The length of the bars or lines indicates the range of temperature for each four-hour low water period.

Considering the observations of local diggers, as to the length of time that Seed Bed #2 is uncovered by the water on each low tide, it appeared that it would be best to compute all information on the basis of the quahogs being exposed to the elements for an average time of four hours per low tide. The length of the lines or bars in the body of the graph indicates the range of temperature for each ) hour-low water period. To give the range of temperature during this period we recorded the tempera- ture reading nearest the time of each low water, and plotted this, along with the temperatures two hours before and two hours after the initial reading.

Barometric pressures and wind speeds and directions are included in the data because of their effect upon the length of time the quahogs would be exposed by the water. Onshore winds, or a low barometer, means that both the high and low tides will be higher than oredicted; while with offshore winds, or a high barometer, they will be lower.

You will notice that the lowest air temperature of the period occurred January 30 and 31, 1951, with air temperatures of -6° F, The warmest period was during the p.m. tide of January ) with air temperatures reading 52° F. The greatest degree of change during any one lj-hour period occurred on January 1 with the temperature ranging from +10° to +3l*. Wide differences can be noted in making comparisons of the temperatures during consecutive tides. Some of these rapid temperatures may well have been lethal to the exposed quahogs in Seed Bed #2. For instance, on December 2) the tempera- ture in the afternoon ranged fran 38° to and the next morning had fallen te a range of 28° to 19°. Other instances of rapid fluctuation and a wide range of temperatures within this period can be readily seen,

In order to record and evaluate the changes that had occurred in Seed Bed #2 since our fall survey, another planimetric survey was made in the spring. Slide #16 is a combination of the map previously shown and the survey map made in the spring. With fall and spring surveys it was possible to make comparisons of the concentration and distribution of the living quahogs. We were also able to show, by counting both living and dead Venus in sample plots, the numbers and locations of the mortalities. It was not possible to make a topographic survey of the seed area because the extreme range of elevations within the area were less than one foot. We observed that elevations and depressions in the seed bed, as well as the position of the seed in relation to high water, had an important bear- ing upon the percentages of mortalities. In general, the sample pilots indicated that the quahogs survived best in the depressions where silt or water covered them during the low tide. Mortalities were also greater near the low than the high watermark. We observed here as we had in other parts of Casco Bay that, where portions of the flat surface were elevated above the surrounding surface, Venus mortalities were high. Differences in elevation are show by Slide #17. In this photo can be seen two stakes of equal length, with both driven into the flats the same distance. In the depression as shown by stake 3, 55 percent were dead; and in the elevated portion shown by stake ), 92 percent were dead. In the entire Seed Area #2, considering depressions and elevated portions from near low to high water, average mortalities were 0.3 percent. The seed bed was spotted with these small depressions, and in'some instances they joined to form extended depressions.

The average mortality rate for areas where depressions permitted the quahogs to remain covered at low tide was 1 percent, while in areas where elevations were higher and the flats were completely drained at low tide the average mortality was 53.5 percent. In some cases mortalities ranged as high as 100 percent. On the other hand, some of the depressions had practically no mortalities.

The spring resurvey of Area #2 emphasized two very important changes that took place between October, 1950, and Mar.= April, 1951. First was the extremely high mortality in the entire area. In Seed Bed #2 average mor= talities of all samples was 0.3 percent. The other fact was the dispersion and displacement of live quahogs as was shown on our planimetric map of the area.

We feel that clam populations can be evaluated in terms of actual pro= duction within a reasonable range of error by using surveying instruments, making a planimetric map, and then considering the acreage involved and the size and densities of the clam population.

In the fall planimetric survey of Seed Bed #1, 6586 bushels were shown in the flats. This survey was completed after 2)\06 bushels had been transplanted from this area. In Seed Bed #2, illustrated by the slides, we found 6637 bushels of quahogs after 568 bushels had been transplanted from the area. In the two seed areas, we therefore, estimated a Venus population

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of 13,223 bushels. In the spring we were able to resurvey Seed Area #2

and found 160 bushels of live and 2,727 bushels of dead Venus. Mortalities in the upper seed bed were 30.3 percent and in the lower seed bed )0.3 percent.

Insofar as the plantings in Maquoit and Middle Bays were made inter- mittently from July 8 to December 6, it is impossible to determine the exact time that any particular quahog was transplanted in considering the growth increments; but it is sufficient to say that growths in some of those quahogs transplanted in the early part of June having a median size of 43 mm. added 12 mm. in growth in one year. Translated into volume increase this means a median increase of 2.21 bushels for each bushel taken from the seed bed.

Had we been able to transplant in the spring of 1950 the Venus that were lost in these two seed beds and assuming survivals equal to those that were transplanted, with comparable growth rates figured to mid summer 1951, the loss to the town of Brunswick in terms of today's prices was approximately $55,000. The loss in Seed Bed #2 alone would be $37,000.

In the spring of 1951 we checked the areas into which we had trans- planted the 3,012 bushels of small quahogs. Because of the small number of quahogs of this size class in these areas, it was not difficult to determine just where the seed had been scattered from the boats. We found that mor- talities ranged from less than 1 percent to 13 percent in these seed islands with the heavier mortalities occurring in places where many quahogs had been dumped in one small area. In several such isolated spots the quahogs were seeded so thick that those in the top layers were unable to burrow into the flats and mortalities occurred.

SUMMARY

In a brief summary of our findings and recommendations for future efforts it appears that:

1. Conditions favorable to high mortalities are created when sedi- ment cover over quahogs is scoured or eroded and quahogs are fully exposed at low water during the winter.

2. Conditions favorable to high survival and better growth are created when seed stocks are removed from areas of high density to sparsely populated flats of normal gradient where quahogs are able to burrow their normal depth below the surface.

3. Density of quahog population is not per se, a direct cause of mortality.

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Exception: i

a. Where density is great enough to contribute to changes of elevation in relation to the normal gradient of the flat. (This proposi- tion has not been established, and there is no definite data even indicating such a condition except where planted stocks had been dumped in large con- centrations in a small spot and created a mound on the flats).

h. Concitions favorable to high mortalitites in seed concentra= tions (even of comparatively low density) are created where portions of the flats are more elevated than would be anticipated from the normal gradient of the flat surface.

5S. Portions of a seed concentration near the low watermark have a higher percentage of survival than do corresponding portions near the high watermark.

6. Where quahogs are located in mounds or bars above the normal gradient of the flat, 100 percent or nearly 100 percent winter mortalities may be anticipated.

7. Conditions favorable to high survival are created when water filled or sediment covered depressions remain during low tide.

8. Considerable displacement and dispersion of living and dead quahogs on Area #2 took place between October, 1950 and March-April,1951.

9. Sediments covering the quahogs! at the time of the October 1950 survey had been removed from the seed concentration by March 1951.

10. The question has been raised - is a seed concentration of high density the result of natural setting in the area or is it the result of transportation of seed by tide, storm or other normal or abnormal conditions from the point of original set to the place of concentration?

Concerning Area #2 this information is availables

a. The presence of a seed concentration in the immediate vicinity of Area #2 was reported by commercial fishermen prior to January, 199.

b. That considerable displacement and dispersion occurred between October 1950 and March = April has been established.

It is likely that the original setting of these quahogs took place somewhere within the immediate vicinty of the present location of Seed Area #2, but it is further likely that considerable displacement of a local nature has since taken place either continuously or periodically.

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RECOMMENDATIONS

As the result of our study of, and experience with, quahog seed concentrations of high density eusiae the past several years we make the following recommendations:

1. Any concentrations resulting from future sets or from the collec- tion and displacement of future sets should be transplanted before growth has created stratification of the population.

2. Transplanting should be made as early as possible after concen- trations have been discovered. (If the 3000 bushels of quahogs trans- planted during 1950 had been transplanted during the late summer and fall of 1948 they would have occupied a volume of some 75 to 80 bushels and the work effort could have been reduced by about 200 man hours.)

3. In order to reduce mortalities of transplanted stocks improved methods of planting the quahogs should be carried out whereby concentra- tions of seed which result in creating points of elevation in the planted area are avoided. The planting should be uniform and spread out well over the area to be seeded.

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INCIDENCE OF INFECTION OF OYSTERS BY DERMOCYSTIDIUM IN THE BARATARIA BAY AREA OF LOUISIANA

J. G Mackin Texas A. & M. Research Foundation and Department of Oceanography, Agricultural and Mechanical College of Texas

Basic to any study of disease is investigation of the epidemiology (or epizootiology if the organism infected is not man). In the case of Dermocystidium disease of oysters every effort has been made to accumulate data which would throw light on the problems of distribution, sources of infection, relation of environmental factors to rates of infection, and relation of intensity and incidence to mortality. It is intended to present in this paper the data from several studies which it is believed are fairly representative, and which will assist in forming conclusions concerning the nature and pathogenicity of Dermocystidium disease of oysters.

The general nature of the disease organism has been reported (Mackin, Owen, and Collier, 1950). It will be sufficient here to recall that it consists of a single cell which reproduces in the oyster tissues by a schizogony-like multiplication of nuclei. Studies on the histopathology of infection have also been reported (Mackin, 1951). These latter studies demonstrated (1) that light infections develop into heavy infections involv= ing the major part of all tissues, (2) that extensive and obvious damage results from heavy infections, involving all connective tissues, muscle, digestive epithelia, ganglia, and others, (3) final stages include develop- ment of multiple abscesses, especially in the mantle, and consequent loss of mantle epithelia.

A primary purpose of this paper is to present data clarifying the matter of incidence in gapers as well as in live oysters. From the stand- point of epidemiology it must be established that intensity of infection in gapers is constantly greater than it is in surviving oysters, and that, fur- thermore, these survivors should show intensities ranging from none through light, moderate and up to heavy, if it be maintained that progressive develop- ment of disease results in death. Conversely, the fulfillment of these con=

Note.=-The Author is indebted to members of the Grand Isle Laboratory staff for collaboration in these studies. Mr. Louis Boswell has been responsible for most experimental work and slide techniques, Mr. Fred Cauthron for photomicrography and Mr. Dan Wray for management of field studies. Dr. Sewell H. Hopkins has assisted materially in many ways. The work of the Research Foundation has been sponsored by The Texas Company, Humble Oil & Refining Company, The California Company, Tide Water Associated Oil Company, Phillips Petroleum Company, Shell Oil Company, and Gulf Oil Company, and this sponsorship is gratefully acknowledged.

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